Home > NRC Library > Document Collections > Generic Communications > Information Notices > 1993 > IN 93­

77

Information Notice No. 93­77: Human Errors That Result in Inadvertent

Transfers Of Special Nuclear Material At Fuel Cycle Facilities

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS

WASHINGTON, D.C. 20555

October 4, 1993

NRC INFORMATION NOTICE 93‐77: HUMAN ERRORS THAT RESULT IN INADVERTENT

TRANSFERS OF SPECIAL NUCLEAR MATERIAL AT FUEL

CYCLE FACILITIES

Addressees

All nuclear fuel cycle licensees.

Purpose

This information notice is to alert addressees to possible sampling program

deficiencies that may arise at nuclear fuel cycle facilities because of the

human factors component of nuclear criticality sampling programs. It is

expected that licensees will review the information for applicability to their

facilities and consider actions, as appropriate, to avoid similar problems.

However, suggestions contained in this information notice do not constitute

new U.S. Nuclear Regulatory Commission requirements; therefore, no specific

action or written response is required.

Description of Circumstances

In August 1992, a licensee notified the NRC that an operator had emptied the

contents of a favorable geometry slab hopper, used to store UO2 powder on an

interim basis, into an unfavorable geometry blender before receiving the

sample analysis for the contents of the slab hopper. The sampling of the UO2

powder in the slab hopper provides one of the controls to ensure that the

moisture content of the powder is below 1 wt(%) H2O. This restriction on the

water content in the UO2 powder is necessary to ensure nuclear criticality

safety in the unfavorable geometry blender.

The licensee conducted an evaluation to determine the cause(s) of the

inadvertent transfer of UO2 powder from the slab hopper to the blender. This

evaluation revealed that the inadvertent transfer occurred as follows:

(1) An operator erroneously assumed that a completed powder release form

lying on a desk common to all slab hoppers was for a slab hopper whose

sample results had not yet been received.

(2) The operator then retrieved a key from the control room and subsequently

released the contents (750 kg of UO2 powder) of the slab hopper into the

unfavorable geometry blender. (This key was supposed to be controlled by
the shift supervisor, as stipulated by procedure.)

9309290006.

IN 93‐77

October 4, 1993

Page 2 of 4

(3) The operator informed the supervisor that he had dumped the contents of

the slab hopper into the blender. The shift supervisor subsequently

recorded this information in the shift log. (At this time, the shift

supervisor should have realized that this was an unauthorized transfer

because he had not signed the powder release form for the slab hopper, as

required by procedure.)

The inadvertent transfer was later discovered when the next shift operator

found an unsigned powder release form (lying on the common desk in the

operating room) for the slab hopper whose powder had been released. The

operator did note, from the form, that the laboratory results for the slab

hopper were within the release limits. The operator informed the supervisor,

who subsequently verified that the results were within the prescribed moisture

limits. The supervisor then completed and signed the powder sampling record

form. NRC was informed of the event in accordance with NRC Bulletin 91‐01.

Discussion

The inadvertent transfer of special nuclear material, in the previously

described event, resulted from deficiencies associated with the human factors

component of the licensee's sampling program. In this instance, the sampling

program was deficient in two respects. Using a common desk for all powder

line paper work represented a less than favorable method to store completed

powder release forms. This led to a situation in which an operator could

easily mistake one powder release form for another. To prevent this problem

from reoccurring, the licensee uses a separate desk to house the forms for

each powder line. (This action has made the inadvertent reading of the wrong

powder release form unlikely.) The licensee's sampling program was also

deficient with respect to securing control of the keys, which are used to

release the powder from the slab hoppers to the blender. By not having a

supervisor control the keys, the licensee created a situation where an

operator's single mistake could lead to an inadvertent transfer. The

licensee's corrective action is to require that the supervisor control the

release keys for the slab hoppers. The licensee's corrective actions are

sufficient to ensure that the following two independent and unlikely events

are necessary before a criticality is possible:

1. The operator mistakenly reads the wrong powder release form.

2. The supervisor misreads the form and subsequently gives the operator the

key to release the powder from the slab hopper.

.

IN 93‐77

October 4, 1993

Page 3 of 4

It should be noted, however, that another possible path to a nuclear

criticality could involve a contingency in which an operator is given a common

key by the supervisor. In this scenario, the operator could mistakenly use

the common key to release special nuclear material from the wrong slab hopper.

To preclude this event, the licensee utilizes individual keys for each slab

hopper.
In addition to the previously described event, there have been other occasions

in which a deficient nuclear criticality sampling program has led to an

inadvertent transfer of special nuclear material. One such case occurred when

a licensee operator analyzed two samples from one tank, but recorded them as

being from another tank. As a result, an inadvertent transfer occurred.

Another type of event occurred, on two separate occasions, in which a licensee

reported the inadvertent transfer of liquid‐bearing uranium to an unfavorable

geometry container. These transfers occurred when an operator mistakenly

entered the analyses for a different tank into the computer.

The previously discussed events illustrate the necessity for licensees to

carefully review their nuclear criticality sampling programs. Licensees

should vigilantly review their respective programs to ensure that the double

contingency principle is fulfilled. This principle requires that at least two

independent and unlikely concurrent process changes occur before a criticality

is possible. For nuclear criticality sampling programs, this requires the

following:

1. Assurance that an operator mistake (contingency) at any juncture

cannot lead to an inadvertent transfer. That is, a second contingency is

necessary before a nuclear criticality event is possible.

2. A contingency must be an unlikely event. This may require one of the

following controls: using color‐coded forms, segregating forms, using

different keys, requiring multiple individuals to inspect results, etc.

.

IN 93‐77

October 4, 1993

Page 4 of 4

This information notice requires no specific action or written response. If

you have questions about the information in this notice, please contact the

technical contact listed below or the appropriate regional office.

/s/'d by Robert F. Burnett

Robert F. Burnett, Director

Division of Fuel Cycle Safety

and Safeguards

Office of Nuclear Material Safety

and Safeguards

Technical contact: Marc Klasky, NMSS

(301) 504‐2504

Attachments:

1. List of Recently Issued NMSS Information Notices

2. List of Recently Issued NRC Information Notices

.

Page Last Reviewed/Updated Tuesday, November 12, 2013